I don't think you have to prove loss sales for trademark disputes. Just a likelihood of confusion. And from the article:

As part of its marketing for the movie, Lucasfilm authorized Filson to run a cobranded campaign to promote the movie and the clothing company’s products, according to the suit. “Lucasfilm and Filson produced a 60 second commercial prominently featuring video clips from the Indiana Jones 5 film intertwined with video clips of actors using Filson’s own products,” writes Devin McRae, a lawyer for Frost River, in the complaint. “Shockingly, one of the intertwined video clips was one from Indiana Jones 5 featuring Frost River’s Geologist Pack.”

I think they might actually have a case. Use of one of their bags used in a lookalike competitors marketing campaign without clearly showing that it's theirs is probably infringement.

Lack of sales might be an argument to be made if we get to damages but I think this will probably be settled out of court for a nondisclosured amount. It'll probably be cheaper for both parties that way.

Provided anyone actually watched the movie long enough to see the backpack.

Ya, don't think many people are dropping $300 on a retro backpack from a movie that bombed.

Doomed to fail.

‘The lead wore our shoes!’ ‘Tom Cruise wore our underpants!’

No way this is actionable. It’s one thing if you have obviously recognisable products prominently onscreen, like a Pepsi can, but nobody’s going to spot your backpack, and not spotting it won’t cost you sales.

Until this article, I didn’t even realise he had a backpack at all (ooh, that’s probably the point).