I bought this plant and put it next to a south facing window on a sunny day. 2 days later I noticed the leaf had this big yellow/brown patch on it. Is this characteristic of being sunburnt or something else?
It needs a much larger pot, but your assumption about sunburn is correct - grown indoors, these plants will like medium to bright daylight, but not direct sun.
It does look as if you're going to have to move it up to a larger pot asap.. these plants get very large indeed so it needs a pot that's probably two to three times bigger than the one it is currently in, with drainage holes. Keep the soil evenly damp, but not waterlogged - empty out any outer tray or pot 30 minutes after watering. Bear in mind it will take up a fair bit of space in the room too, so find a spot for it where it gets good daylight, away from heat sources, and has sufficient room around the topgrowth for it to spread itself out as it grows. More info here https://www.hallmarkchannel.com/home-and-family/how-to/how-to-care-for-indoor-elephant-ear-plants