At first, Thermal and Laser can feel like they belong to a broad topic instead of one exact family, which is why typed-category boards often look looser than they really are at the start. One tempting read was "a broader umbrella topic". Thermal, Laser can sound like they belong to the same general area before the board tells you what type of thing each clue actually names.
Dot matrix pushes the solve down to one exact type-level category instead of a vague umbrella topic.
Another nearby bucket was "a loose mascot or named-entity cluster". Capitalized or specific-looking clues can tempt you to group them by surface familiarity instead of by category level. The solved board works because every clue becomes a member of the same typed family, not because they simply feel related.
Once the board turned into a question about what kind of printer each clue could be, a category board focused on printers stopped sounding generic and started behaving like a real category test. Examples like "Thermal printer" and "Laser printer" then read like recognizable members of the same set rather than isolated references that merely share the same mood.
3D printer, Dot matrix printer, Inkjet printer read like named members of the same typed category, which keeps the board precise all the way through instead of letting it drift back into a broad topic bucket.
The answer was "Types of printers". More precisely, the board resolves as a typed category where each clue names a specific member of the same family around Types of printers, which is why "Types of printers" fits better than "a broader umbrella topic" or "a loose mascot or named-entity cluster" once the full set is checked.