I find once you've been tracking your macros and weighing your food for a long time you get pretty good at guessing. It's obviously true you need to eat more to gain weight but honestly it doesn't always work. When I was 16 to 18 I was eating 3,000 calories per day when my maintenance was about 1,700. Over the course of this 2 years I gained about 3-4lbs, and I was lifting heavy as well with compound lifts and eating perfect macros. That said, I have the fastest metabolism of anyone I know. Lived with 3 guys who are all much bigger than me last year and ate twice as much as them al year and didn't gain a pound and they got fat. Wasn't even doing cardio, no joke. So it is possible to have a very, very fast metabolism. That said, at 20, mine started to slow down every so slightly. Even now if I go on a dreamer bulk my gains are mimimal, but better than before.
Why not dispute his FACTUAL comment instead of making a smarmy contribution? Virus is bang on the money. You work out? Nah didnt think so...