Your barber didn't mishear you. When you asked for a 2 on the sides and walked out looking shorter than expected, the number wasn't wrong - it just wasn't the whole picture. Guard numbers are a measuring system, not a style language, and knowing the difference will change every haircut you get from here on.
A clipper guard is a plastic comb that clips onto the blade and controls how close the teeth get to your scalp. The number is shorthand for length. A #1 leaves about 3mm of hair. A #2 leaves 6mm. A #3 sits around 10mm, a #4 around 13mm. By the time you're at a #6 or #8, you're looking at a full inch or more - territory where most guys would just call it "long on top." The half guards - #0.5, #1.5 - exist to split the difference when a full number jumps too far.
Here's the catch: those numbers assume a standard clipper at a standard setting. Andis, Wahl, Oster - they're not perfectly calibrated to each other. A #2 on one brand can run slightly longer or shorter than a #2 on another. That's before you factor in hair texture. On straight, fine hair, a #2 sits flat and looks quite short. On thick or coarse hair, it can look almost full because the strands push outward instead of lying down.
The upshot is that "give me a 2" tells your barber where to start, not where to land. What actually moves the conversation forward is showing a photo, describing the skin exposure you want (none, a little, a lot), or referencing your last cut - what you liked, what was off. A good barber can read those cues and dial in the length that works for your specific hair, not just your number.
Guard numbers are a tool. Communication is the actual haircut.