On reddit at least it seems like everyone under a certain age doesn't use the term at all and just calls everything, including websites, an app.
In the 2020s, when 90% of software development consists of using a database, tooling supplied by various open source projects and some choice of web front- and backends to create a front end to enter/edit/view the database contents, the results are called "apps".
plus ça change, plus c'est la même chose
Though if you call the PNG file that's a menu for your restaurant an app, that's just wrong.
And that's why they are wrong. If anything and everything can be called an app then the word lost its meaning.
Definitions of the verb apply from https://en.wiktionary.org/wiki/apply#Verb:
2. (transitive) To put to use; to use or employ for a particular purpose, or in a particular case
to apply funds to the repayment of a debt
3. (transitive) To make use of, declare, or pronounce, as suitable, fitting, or relative We need to apply the skills we've learned to solve this problem