Understanding Kraken Trades API (market/limit)
Indeed they don't specify what it means, but the only sane option is that market/limit tag comes from the type of order that closed the deal.

For example there are two lowest sell(ask) orders hanging in the order book:


0.05 BTC at 2000 EUR
0.03 BTC at 2300 EUR


I come to Kraken and place a Market order, buy(bid) for 0.07 BTC, thus the first trade will be for 0.05 BTC, and the second will be for 0.02 BTC. Both will have designation 'market'.

It is possible, however that I want to buy some bitcoin, (let's say 0.9 BTC), but not higher than 2300 EUR. Then to make sure I don't pay more than planned, I make a LIMIT order and the two awaiting orders are matched to mine and what is left of my order amount may hang in the order book on the Buy side. In this scenario the trades as seen via API will have designation 'limit'