Basic answer is no because Mr Van Gogh is long dead and any copyright he ever had is now expired. But let’s say he only died a few weeks ago.
Otherwise, it depends what the sunflowers you painted look like. You’ve seen the work that it is alleged you copied, so stuff that looks a lot like copying is assumed to be copying, roughly speaking. If you produced a work that reproduces substantial elements that were original in Van Gogh’s work, then Van Gogh has a case in copyright infringement. That can include the overall composition of the painting, some particular brushwork, etc. Techniques are not protected by copyright (that is generally the domain of patents, but afaik there are no extant patents on how to use a brush), so you can copy the techniques as much as you like, as long as you are not copying actual brushstrokes to reproduce the painting.
Copyright is concerned fundamentally with the degree to which you are stealing the market for the original work. It was created to allow authors etc to profit off their hard work, rather than labour for years writing a book only for someone else to make all the money from selling it. The existence of copyright makes it possible to make money despite the fact that copying someone else’s work has always been easier and cheaper than making something new. You could spend ten years writing a book, and it would take someone a day to print a copy, and twenty other printers could do it and none of them would pay you… so why would you write a book in the first place unless it were a political/religious pamphlet? To guide your interpretation of copyright, think about the degree to which you are stealing a market for Van Gogh paintings. If you produce a very close replica, then yeah, you are stealing some of the market. Photographing the painting and selling prints does the same thing. Producing something close from scratch without reference to the original is absolutely fine, if there is no copying then there is no infringement. The copyright statute just doesn’t want you stealing Van Gogh’s market for his own works using the crutch of copying his stuff, and through no original effort of your own.
Obviously AI art is a huge problem for this fundamental goal, because it hides the copying that it does. Someone selling a copy of your book without a license is easy to identify. AI art lets you take some art you like, launder it a bit, and then use it in your marketing materials without the original artists being able to notice the infringement and sue you for it. Fundamentally it is like money laundering, the same way AI data analysis has often been used for laundering human biases. That’s a huge problem and really subverts the entire intention of copyright. It steals the market and hides it at the same time.
You can also see how using an AI tool to launder images is just copying with a small amount of original human labour curating the input works. You can have some credit for your labour picking them, but you can’t really pretend the source images’ copyrights just disappear. The only issue is which humans are owed royalties. There’s a lot of debate going on about whether computers doing art is just like painters studying, just like you said, but if you analyse it as the laws do only in terms of the humans involved, you have a bunch of artists, and someone operating a lever labelled “mix these paintings so nobody can recognise my IP theft” that will vastly outpace their production and steal 99% of the market very quickly. It’s the invention of the printing press all over again.
If the copyright laws are too difficult to apply (eg an AI painting is such that it has laundered away any ability to pick out which bits infringe a human’s original painting used as input) then rather than everyone throwing up their hands and admitting defeat, the laws will probably change to better serve their original purpose. For example, AI paintings may have to pay royalties to every single artist used as input regardless of whether individually identifiable instances of copying are visible in the output.
