Chaste or Pure, what's the difference?

Yesterday I watched Vivah ( विवाह, Marriage). The groom (Shahid Kapoor) is a rich boy from Delhi, whose family is from Uttar Pradesh. The bride (Amrita Rao) is a simple girl from a small village. The groom's brother and sister-in-law (Sameer Soni and Lata Sabarhwal) tease him by telling him she won't understand his slangy Hindi mixed with UP dialect and English: he'll have to speak pure Hindi. It's a little running gag that he can't finish a sentence, while they both can - and do, including finishing his. (Fortunately for him, she's not nearly that sheltered.)

What was neat was that the subtitles told us when any of them was speaking "in pure Hindi" - as well as using somewhat more elevated English (including 'thy') when they were doing it.

What was funny was that the subtitles actually said "speaking in chaste Hindi".