There are 4 levels of sexual content in anime/manga: Fanservice, Ecchi, Smut, and Hentai. You have to take into account the length and level of the actual lewdness, the time in between, and the seriousness of it. Take what i say with a grain of salt, not everything is clear cut and there are a few exceptions, but it does fit about 99% of all manga/anime.
TL;DR Ecchi is comedy, Smut is serious.
Fanservice is the bathscene or stumbling upon someone changing once or twice in a single cour. Usually r12. Take any shonen ever.
Ecchi (regardless of genre) is the groping, girls changing, half naked, the "accidents", thirst, showing of curves, pantsu, sucking on a dick shaped object etc in every episode/chapter, but almost always censored to hell and back on the tv release, they might show some nipples on the bluerays. However they never commit to actual intercourse due to some "hilarious" reason, the mc is dense, for some reason wants to become a wizard at 30, or at most once when its merely implied by a time skip or like the monogatari toothbrush scene. Usually its just part of the comedy cus japanese people somehow find it funny. "MC fell into a girls chest while getting her wet, haha funny". It's still r16.
Smut can go 3 ways, non-nude, nude and proper story. For the first two cases one or more character (or reader) is in one way or another getting off from whatever is happening, be it sexual acts or just the fetish. Mostly the fetish is the full focus and is dedicated the emotional part of it. Usually its serious and serves as actually plot, character development, or world building. However it is not meant to be fapped to. For a smut with proper story the sex last a page or two, or is few/short and far in between and could pass as r12 if it wasn't for the sex. Originally, smut means porn in the form of pure text, like fifty shades of gray (it's bondage porn for women, if you didn't know). Can be r16 but is mainly r18.
Hentai get straight to the point and has about 12-25 pages per scene and have 1-2 scenes per chapter, and the sole purpose is to be jacked off to.
I wanted to post some links for a few manga per category to better show the range and ballpark but i couldn't find a few of the good examples that iv seen over the years so i wont bother unless requested.
As for what this manga is, id argue its ecchi, since smut is not men't to be a comedy.
