Lovely looking sweater.
Aran has different meanings.
A yarn used for knitting can be of aran weight which means a certain thickness, but may not even be wool. I can easily buy aran weight yarn made of acrylic or cotton. So that’s one thing, it wouldn’t be untruthful to call an acrylic lace vest aran so long as it was aran weight yarn. And a lacey vest wouldn’t offer much protection from the elements.
Aran is also a style, the cables, and stitches used which give a certain fashion look. An aran style sweater can be of that fashionable style without even being in aran weight yarn, or made of wool or made in Ireland.
If you read around the Internet you will find many stories and myths about the aran sweater, and some sites which explain the myths have been debunked. Many will maintain the myths as it’s nice to have a story to sell a sweater.
To be honest you probably wouldn’t want a “real” traditional aran sweater. An item made for work wear would be coarse and hard wearing, coarse wool from the local sheep (which would have been a coarse wool, not the soft merino often used now) which would be unwashed to maintain the lanolin to help repel water.
Modern aran sweaters are more preferable, made with a much softer sheep wool, better than the coarse wool which would have been stiff, itchy, heavy.
Most modern aran sweaters will be machine made rather than hand made which effects how loose the knit is too. Not as thick as you were expecting.
In terms of your sweater, as “Aran” sweaters are a fashion item now rather than a work wear item, it’s down to deciding for yourself if you like what is being sold. Perhaps you would prefer a hand knit fisherman sweater which you would likely need to pay several hundred £$ for and advance order then wait for it to be knit.
Slightly different subject but still relating to work-wear. I’ve worn army surplus shirts, sweaters, combat trousers and overalls in my work life (not in the armed forces but I wore these for their hard wearing properties) and personally I couldn’t bare to wear new items as they were SO stiff and coarse. The army surplus items were previously owned and had been worn-in making them softer and easier to move in. Combat trousers are now a fashion style and can be made in any type of fabric with the combat style - similar story - a fashion item wouldn’t hold up to the amount of wear and protection I needed from my combat trousers and overalls.
Similarly denim jeans used to be really thick and coarse work-wear and now are an everyday item which many people want to be thinner, lighter, stretchier, softer, easier to move in, and they don’t need the protection of the very thick denim which was once used.
If you are not happy with the quality of your sweater you could return it perhaps and look out for a different sweater. Or layer up with a wool skinny rib underneath for extra warmth.