A question about grammar: A pair of jeans means there is only one piece. A pair of jumpers, there are two pieces.
First of all you are correct.
"A pair of" is one of the interesting little excentricities in English.
Most pairs are clearly two separate things. But a few "pairs" are single units.
With a little imagination, however, you may notice that these "single pairs" consisit of two, usually identical halves:
a pair of trousers/pants/jeans (note: each pair "consists of" two legs )
a pair of shorts
a pair of pajamas
a pair of suspenders
a pair of glasses/sunglasses
a pair of scissors
a pair of tweezers
a pair of pliers
Hope this helps