Bitcoin can be regarded as currency and it can also be regarded as asset too, because it can be use for transaction as a medium of exchange and it can be kept for future use which are both currency and asset
Bitcoins can be asset and currency, actually depending on the users of bitcoins what will be done with bitcoins, although the main purpose of bitcoins is currency doesn't mean it is must. Because Bitcoin is based on the community they are free to consider bitcoins as an asset or currency, that is uniqueness of bitcoins everyone can be free to participate giving their opinions about the bitcoins.