A ligament is not a tendon.
Ligament connects bone to bone. Tendon connects muscle to bone.
Big difference.
Ligamental issues in the digits are fairly common. Tendon issues in the digits are less common.
To a writer who seems to be guessing and doesn't seem to know much about anatomy, it could be either one and a 50/50 shot of being right especially befre an official annpuncement (ligament) is made.
If the writer knew a smidge about anatomy, he could have written " After x-rays came back negative for bone breakage in Stafford's thumb, signs point to a possible ligament injury but wait to be confirmed."
What's so hard about that?