Why did my market order get executed as a Limit order?

There could be 2 reasons:

1. Due to market price protection measures introduced by Exchanges, for some instruments, market orders are sent on the Exchange as limit orders.

2. In case of illiquid scrips, where the bid-ask spread is extremely high, there are chances that the market order gets executed at a freak price, i.e. at a price far away from the current market price. In order to prevent this kind of an adverse execution, Exchanges have defined a price range which is at a certain percentage above and below the last traded price.