Is it normal that a Macbook (12) service battery shows after charging it using USB wall plug (in hotel) on one occasion?

Does you laptop have USB-C ports?

The quality of third party non-Apple chargers and cables can be severely deficient and could cause damage to the laptop.

I've also seen multiple reports on these Apple forums where users have noted the battery status has shown as "Replace Battery" and then reverted back to "Normal" again. I don't know if this is a macOS bug or whether some newer systems have some odd behavior or battery reporting issues. Or perhaps some newer batteries may have a yet unrecognized flaw.

Try running the Apple Diagnostics to see if it reports any issue with the battery.

I have an Early 2015 12" MacBook and am now on my 3rd battery, that wasn't covered under the expired Apple care. The 1st battery was replaced under warranty. It's probably border line and in need of replacement and it has no relation to it being used in a hotel. Keep a close eye on it as failing batteries can swell and damage the logic board and the case, in which case you'll be looking at way more than a $200 battery replacement.

Take it in for service to be sure. Are you still under warranty? Do you have Apple Care?