Splash LP can promote you to another Tier on another role -- Is this intentional?

So -- I was originally in D4 in support and G1 in Jg. I was at 100 lp but did not do placement games for jungle.

I'm a support-only player so I wasn't really interested in playing any other role.

An interesting thing happened. I won a game in D4 on support and skipped placements in jg and got promoted to P4.

I didn't screenshot but it said that I was promoted because of performance on other roles (aka support)

Obviously, I am a bit of an oddity in terms of the gap between abilities as a support and other roles, but I'm wondering whether anyone that is within a couple tiers of each role has experienced something similar? If so, this may be a climbing strategy -- get your role up to 100lp and not do placements and just try to win another role.

I'm just trying to get feedback from other people due to this not being covered in any kind of official notes.

Thanks in advance.