Leave it to Aquarius to pay close attention to the aura or vibe they feel from others. With them, its a hit or miss and this is often determined by that immediate interaction they encounter with a specific person.
You’re feeling the energy around others. The frequency of the aura can be strong or weak and fluctuate. It’s an energy transfer. The heart aura area is 60 x stronger than all the other main chakra aura energy spots.
So emotions and feeling, moods, temperament, can all be felt more easily than say, picking up on subtle thoughts of another. Which is possible too of course, but takes practice.