Well for one instance he's no longer fooling around, he also recovered from his injuries and probably has been practicing a lot, also his drunken style is really strong, we see that with his sister too, so yeah
If I recall correctly, Suiryu never even used drunken fist during the tournament arc (or at least not like he did in this fight), while Garou is seen frequently using his dojo's style when he needs to fight heroes. There was a clear difference in their convictions to be stronger. The Suiryu back then didnt take anything seriously, but with his talent, he'd probably progress fast if he actually tried. For me, the only truth in this universe is that no one is on Saitama's level, nevermind how strong they become
I think its because garou mentioned he lost / forgotten all those secret techniques that he unlocked when he turned to a monster. Also so of Garou's techniques at the time were forbidden techniques that silver fang hide. My guess is he is trying to completely abandon the forbidden techniques he's not allowed to use because he is trying to train the proper way to regain silver fangs respect. Also because he's not trying to fight as if he's a monster
I haven’t read in a while so i might be wrong. But how is suirya even close to Garous level? We saw Garou fight against things way stronger than suirya but now all of a sudden their on the same level?? Sorry for articulating this badly, just doesn’t make sense to me