> The author is blatantly wrong wrt "jeans and hiking", but otherwise firstly doing the "discount" version of a thing to learn the thing is the right approach.
Wildly disagree, but I suspect when they mention hiking, you get a specific idea or degree of what that means based on the type or terrain you regularly experience. While there are pieces of gear I wouldn't go into certain situations without, what those situations are and what that inventory looks like are pretty variable.
To anyone who'd like to try, jeans are fine, sometimes they're inadequate, sus out the trail and the conditions, don't let a lack of non-jeans prevent you from trying, but also proceed with sensible caution and learn to know your surroundings. DO NOT RELY ON GOOGLE MAPS EVER EVER, get something else or an actual map, and don't expect to have cell service.
If you have no fitness at all, start small (1-3hrs, flat or a few hundred meters of elevation gain), bring at least a liter of water, do it with someone or tell someone where you're going, go early during the summer. I'd advise that the most generally applicable requirement in terms of gear are shoes with grip of some kind (I use relatively inexpensive trailrunners, boots aren't as nimble but can be better depending on variables), then a basic headlamp unless you're in the north in summer, compass maybe, a lighter, and calories, everything else either depends on environment or other variables and you get a sense for it over time. A 20L day pack is helpful, but a regular backpack is just fine as well.
For pants, it's not rare for me to just bring breathable shorts from Lulu and normal Levi's jeans, switching between them as necessary, but sometimes just one or the other, and nearly always in a basic-ass cotton shirt that I just take off because I can't be bothered. The only people who mention my attire are the ones who never do it. Your mileage may vary.
Lastly, I personally never bring headphones, don't listen to anything, and keep the phone off or in low-power mode with GPS on. I'll check in at a halfway point if it's a long day, but when I'm in nature I'm in nature, and I'd recommend the same. It's empowering to learn to be capable in nature and with nothing but your own thoughts.
Edit: Mentioned by someone else, a guided adventure as an inexperienced outdoors person is not the time to deploy my advice, respect their requirements, they know more than you whether it is or isn't ultimately necessary. My advice applies outside that context, where you're not someone's else's liability. Read my advice as analogous to "you don't need cleats to play soccer, unless you're joining a team, especially as a noob, so get out there and kick a ball around"