I think his point is this. And it is a completely valid one. You are 100% allowed to break up hard cover sessions. (you don't have to play Curse of Strahd in one sitting)
Absolutely true. In fact, I don't know that I've ever met a group that finished any hardcover in a single session, so I'd say this is not just allowed, but required.
If you do so you are required to award xp and distribute items at the end of each session (this has been specifically stated that you can't leave items "floating, or party loot" that isn't claimed by players).
Also true, precisely because each session has to be considered to be able to stand on its own. This does make for some awkward situations, such as the wizard not being able to play at the session where the spellbook is awarded as treasure, but for a significant number of treasures, there are workarounds -- for instance, trading permanent items, allowing the wizard to use downtime to copy the spells from the spellbook, etc.
Next week rolls around, not enough people show up. I give up finishing the chapter as no new players want to start mid chapter.
This is a 100% legit and legal thing to happen. As a player or a DM you are not required to continue in any adventure, and you are allowed to split hard cover adventures over multiple sessions.
Here's the problem -- say you weren't running a hardcover adventure, but a DDEX/DDAL module. Refusing to complete the module effectively locks out the players who played it the previous week, but now won't get a chance to finish the module, because they can't go back and start the same adventure over again. Because of this, most locations that allow session-based DDEX/AL play run the same modules until they are completed, even if players miss sessions.
Don't screw over your committed, consistent players in favor of transients who don't necessarily bother to show up week to week. Commit to completing the adventures you run, even when it's inconvenient for new players, because hopefully those new players will find themselves in the position where they will be the committed, consistent players rewarded by your DM style.
Regardless, though, the 'no loot runs' rule has to be enforced by the DM or it doesn't effectively exist. If the DM clearly isn't enforcing the rule, then you should have the option to do so by not claiming the rewards from that session, if you choose to.
--
Pauper