Yes, it looks like you have the later sealed cooling system with expansion tank which may be original or could have been a retrofit.
The cap on your rad looks very 'crusty'. When your problem occurs, are you losing coolant from the expansion tank or from the rad cap (where it is crusty). My 142E has the same rad seal cap as your 1800. Years ago I did a complete resto on my 140 which included a new rad cap. I discovered that the new rad cap was a leaker because it was manufactured incorrectly - the retaining ears on the cap were positioned incorrectly with the result that it did not seal tightly against the filler neck on the rad. I had to cut a couple of sheets of brass shim to fit under the rubber seal of the cap to get it to fit tightly. The cooling system is designed to operate under pressure which suppresses the boiling point of the coolant. If the rad cap is not sealing you will get premature coolant boiling which causes overheating which causes more boiling ..... and eventually coolant dumping out on the floor. A pressure test of the cooling system would confirm whether the rad cap is leaking. However, visual inspection of the underside of the rad cap may also reveal that it is leaking. During the work on the car the gasket under the cap may have been disturbed or damaged resulting in a sealing failure.
If the expansion bottle is venting due to overheating the venting will occur at the top of the bottle around the pressure cap. From the photo, there are no obvious signs of venting around the top of the bottle; but, things are a little dirty so hard to tell. A crack in the expansion bottle can result in coolant loss; but, the original round expansion bottles have been pretty durable. The much much later Volvo tanks with slab sides - not so durable.
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