Hey!
I don't have any explanation, the set looks like any other in the same dat:
<game name="Swimming Database (19xx)(Col Oats Software)[BAS]">
<description>Swimming Database (19xx)(Col Oats Software)[BAS]</description>
<rom name="SWIM.BAS" size="6912" crc="7d9cce7d" md5="c48d21eefb0ae0bad4e3299151c1a160" sha1="559ee621f285b3f6cbd58618c0e480d7747a2ded"/>
</game>
Do you have the exact file? The hashes match? It may be a bug of one of the tools or even a bug in the dat, although everything looks ok.