That's not necessarily true. Ever heard of PV=nRT? You can very well have an isovolumic transformation where the temperature increases thus leading to an increased pressure.
Temperature is really the measure of kinetic energy, or how quickly individual atoms and molecules are moving, so when the temperature is increased, they move faster and farther apart.
Temperature is vibration and movement at the molecular/atomic level. The more movement, the more space is needed to move. One proof: In the case of vortexes, this throws the faster-moving warm gas to...