One of the most important characteristics in a partner is authenticity. If they didn't think of getting you flowers themself (and had to use an app), is that real?
In receiving flowers, the value the recipient gets is not so much the flowers themselves, but by what the gift betrays about your mind state. This authentic information about your mind state is what makes the act “real”.
So it is reasonable to consider the act less real or even a bit deceptive if the mind state that you’d first expect the act to imply (they care about me and thought to get flowers) does not reflect your true mind state (they cared about me enough at some point in the past to set up this app).