This is best explained with an example. Let's say you carried out these 3 transactions:
Bought 2 BTC in January
Bought 3 more BTC in February
Sold 4 BTC in March
Here, even though you only had 1 sale transaction, you would see 2 disposals on your tax report. This has to do with the way your costs are calculated (FIFO, LIFO etc).
As your transaction count rises, this difference can get larger:
Bought 3 BTC in January
Traded 1 BTC for 8 ETH in February (1 disposal)
Traded 0.5 BTC for 7 ETH in March (1 disposal)
Traded 1.5 BTC for 15 ETH in April (1 disposal)
Sold 30 ETH in May (3 disposals)
In this example, you would have a total of 6 disposals for only 5 transactions