The history store has the following key format:

#define WT_HS_KEY_FORMAT WT_UNCHECKED_STRING(IuQQ)

which is

btree_id
key
hs_start_ts
hs_counter

The decode tool unpacks these bytes and prints them as:

  <packed 41 (0x29)> <packed 1 (0x1)> <packed 11 (0xb)> <packed 7608437202250366991 (0x699699530000000f)> <packed 0 (0x0)>

Since this data format should not change we should do a better job of printing these values so they are clear to the user.