I just had a look an that does seem to match with the example in the API documentation for getting a Tweet - a contraction of the content and inclusion of an ellipsis and a URL.
{
"created_at": "Wed Oct 10 20:19:24 +0000 2018",
"id": 1050118621198921728,
"id_str": "1050118621198921728",
"text": "To make room for more expression, we will now count all emojis as equal—including those with gender and skin t… https://t.co/MkGjXf9aXm",
"truncated": true,
This also occurs in [the Tweet data dictionary](https://developer.twitter.com/en/docs/twitter-api/v1/data-dictionary/object-model/tweet), where the same example is used.
In neither location does it seem to actually provide any further details about how the value is generated other than to say that it is:
The actual UTF-8 text of the status update.
… which is false based on the discrepancy between the post and the return.