If D&D was a car, I would say that 5E has the paint job and outline of 2E, but it's a whole different interior and engine.
It has the same outward facing names of things, but the mechanics and playstyle are nothing alike.
It's like this - both of them have class levels up to 20th and spell names up to 9th level, but 2E approaches magic as a rare quality that occasionally springs up and is somewhat terrifying when it does (cursed items, spells that age you or have other negative effects, strict limits on spellcasting, d4 Wizard hit points and more). The lore and playstyle really tends to push the narrative that overall (you can feel it in how the designers are always at the ready with the banhammer against magic), magic isn't really that common and the supernatural is quite distinct from the mundane world. In 5E, its everywhere and in everything - you can't swing a wand without running into something magical.
Likewise, in 2E combat is in a transition state from 1E as being a punishment for failing to correctly scout ahead, negotiate or problem-solve to avoid fights; you and your group are outnumbered and outclassed almost all the time. There's a bit more push against the requirement of 10 foot poles, but encounters still tend to discourage a direct approach. 5E, on the other hand, not only encourages you to solve every problem with violence, but that the group should almost always be able to overwhelm the opposition in a straight-up fight.
And, as others have noted, rest and recover are two comletely different animals between editions. 2E is really about wearing down the party's resources until the group is forced to rest, and then punishing them with recovery periods that match the mundane world. 5E use action movie rest and recovery options, with no long-term negative effects. It's quite stark.
You can really tell with 2E in how the whole world seems to start falling apart when you get into the double-digit levels. The game's no longer gritty, and the designers just seem to be unwilling to accept and build adventures around that fact. They still try to treat it the same as lower level.
5E can get just as wild with abilities and powers, but the worldbuilding much more accomodates higher level characters and their abilities.
So, if you just look at the surface, the two do appear very similar. But in actual play, they are two COMPLETELY different animals. And, in most ways, I prefer how 5E actually runs at the table.
