This isn't uncommon in Google results. The other day I wanted to double check that Steve Carell was Gru in Despicable Me because I'm awful at remembering celebrity names. The search "despicable me cast" got a list where he didn't show up until you scrolled way down, past someone else (who appears to be a dubbed version's lead) credited for the role. I'm guessing the issue is really in whatever dataset they source movie casts from.
Tom Cruise didn't use to show up in the cast for 'Top Gun'. They did however list all other actors, including unnamed characters. It's since been corrected, although he currently isn't the first cast member listed.
Is John Hurt controversial in some way that's not obvious from looking over his Wikipedia page for a minute that he'd be intentionally omitted?
I think this is because Google compiles these cast lists based on search proximity prevalence. So if you look up some actor and a movie in the same query many times it starts to assume the actor is in that movie. Maybe they combine this with some base scraping but I think it's highly unlikely they use some API or hand craft the lists.
I always assumed it was scraped from IMDb or TMDB. It usually includes both character and actor names together, which seems hard to glean from search queries alone. Ordering them based on search volume could make sense though.
Definitely possible. I think they got a lot of backlash from scraping a music lyric site without permission so they might be more hesitant to do so in other areas unless they have clear cut permission.
So if there were two actors that were commonly confused, likely they'd end up showing as if they were both in the same movie.
Sounds like a great way to get inaccurate results.