Recently, I'm interested in Apple's AirDrop feature. After some research, I found that it uses low energy bluetooth to discover other devices and establish a WiFi connection. However, when you are already connected to a WiFi network, will it temporarily disconnect or are Apple devices able to establish the temporary file exchange network in parallel? How would it be possible? Can a single WiFi card establish multiple WiFi connections or do they use an extra/special WiFi card in their devices?
Yes, supported Apple devices are able to be connected to a WiFi network (i.e. an access point) and communicating via this "temporary" peer-to-peer network simultaneously. The protocol that is used is called AWDL (Apple Wireless Direct Link).
A single WiFi "card" can do this, yes - you do not need two WiFi "cards".
I would say that Apple popularized this type of connectivity, but today it is also possible to do something similar on non-Apple systems. I.e. this is not dependent on some special "Apple WiFi chip". The most direct comparison is the WiFi Direct feature found on other systems (for example Android phones, Windows laptops, etc). Some WiFi chipsets supports WiFi Direct while simultaneously being connected to an access points - others do not.