The growing "head" is just the furthest end of each individual vining stem :-) It may not look like it will produce additional growth (and it might not do a lot more this season, as the plant is busy developing its root system) but it certainly could. And will next season :-) Even when cut back hard in late winter, which is a recommended practice for ALL newly planted clems, regardless of pruning type.

It doesn't look bad for a newly planted clematis though if it was previously in an area with fewer brightly reflective surfaces, it may be dropping leaves that aren't able to adjust to the new brightness.

Did you plant a bit deeper than it was in the pot? A clematis is one of the few plants that like this treatment as it encourages new stems to grow from below ground, so you may see new stems at the plant's base.

Do you know what kind it is? Usually it's suggested that new clem plants get cut back to a few leaf nodes per stem, which will encourage growth of more stems and a denser growth pattern. Some will come from below ground, some from the top of vines, and some from secondary stems at previous leaf nodes, especially if the top of the vine has been pruned. Yours looks like perhaps the vine was cut or is that just a product of the photo? No need to specifically prune off the seeds, which IMO are ornamental in their own right, though it isn't a problem to do so. Type 2 prune plants regardless of age do well with a light prune after bloom since it encourages new growth and late summer or fall rebloom in areas with a longer growing season than where I am.

IME clems usually put a lot of growth into roots the first season, though it will vary some depending on how large it was to begin with. I plant smaller clematis since most of mine are mail order, and I really start to see a lot of above ground growth the second year, though they do grow some leaves and vines the first year.

It would be far happier with an organic mulch such as bark mulch or compost than rocks. The combination of cement pool deck and rocks can probably get hot, and if there's landscape cloth (which often gets put under rock), that will not help since it tends to interfere with movement of water and nutrients.

A wire tellis will be easier for the clematis to climb than the wide trellis pieces since it climbs by wrapping its leaf stems (petioles), so does best with something pencil thickness or less. You may have to periodically fasten the clematis to the trellis.