There was the SP1, and SP1 Carbine. The SP1 came as everyone described; triangle handguards, either a birdcage or 3-prong flash supressor, large front hole, no fences, mil-spec FCG pins, no forward assist or shell deflector on the upper.
The Carbine had the same features, except it had round handguards (Colt, or anyone else for that matter, NEVER sold a factory civilian AR15 with anything other than round handguards on thier carbine models), a 16" barrel instead of a 20", a metal 2-position collapsing stock covered in vinyl, and a birdcage flash supressor. Depending on when it was made, it might have an A2 cage. (Or, someone just stuck on an A2 cage, whatever...easily fixable)
They all had A1 sights.
So, yes, what the person is describing, is a Colt SP1 Carbine.