A digital sensor is an array of pixels. There are lines between pixels...assuming no AA filter, in which case there are lines between filter cells. The objection is a “No true Scotsman.” A camera consists of an aperture for collecting light and a medium for observing the collected light, e.g. the cameras obscura and lucida. If the collecting medium can record the collected light, it can produce photographs, either still or moving.

It’s worth noting that astronomical pictures often consist of multiple overlapping photographs. And I guess it’s plausible to describe a digital sensor as capturing many one pixel photographs.

Microlens arrays have been standard for years and increase the fill factor to ~100 %, so the argument is kinda bogus. In any case, the gaps between adjacent sensors in a "raft" are much bigger than the pixel pitch, and the gaps between rafts again larger, so the argument is kinda moot either way.

As long as the lines between pixels/cells are smaller than a wavelength, there are no gaps between cells, only decreased sensitivity.

Thanks to microlens arrays, moire filter, and sometimes the sensor outresolving the image, this is not actually an issue.

It ia a single camera with multiple CCD detectors on a common focal plane behind a shutter. It is not a single CCD on a common focal plane. Should there be such a 3.2GP sensor, the noise would be abysmal, silicon would be huge, pixels tiny, and it wouldn’t be all that interesting for astronomy. Note that each 16MP sensor is physically quite large as well.