This is a matter of interpretation. Many of us who’ve seen the film many times have always interpreted it as Dark Helmet ordering Spaceball One to go faster than it ever has (“Ludicrous Speed”), then pushing throttle all the way (past “Ludicrous”), and the ship accidentally going faster than even Ludicrous (“to Plaid”) and thus overshooting Lonestar and the gang.
I think reasonable people can interpret it either way. One other variation that seems plausible is that “plaid” is what happened when you go the fastest speed within the “Ludicrous” range.
Either way, I think this is all reading way too much into a silly joke