The 'growler' in this case is slang for a bucket. People are filling bottles and jugs nowadays. I can't find a single reference of anyone using the term 'growler' to refer to anything other than a pail or bucket. I have, however, seen many uses in which it is simply called a bucket.
All signs point to misuse by beer nerds:
no you're right that buckets for beer used to be called growlers but so did jugs/pitchers.
you're not allowed to sell beer in buckets any more for pretty good reasons... so the jug form is ubiquitous today... the term growler for a vessel of beer has been around since the 1800s...
i mean you realize language changes right? growlers used to be more known for buckets and now they're more known for jugs...