(From: http://www.theopedia.com/Systematic_theology): Systematic theology is a discipline which addresses theological topics one by one (e.g. God, Sin, Humanity) and attempts to summarize all the biblical teaching on each particular subject. Sometimes called constructive theology or even dogmatic theology, the goal is to present the major themes (i.e. doctrines) of the Christian faith in an organized and ordered overview that remains faithful to the biblical witness.
Systematic theology integrates biblical, historical and sometimes philosophical theology into its methodology.
The first paragraph is fine and, indeed, the Christadelphians have a document that could be defined as "Systematic Theology" if we were to leave the definition at the first paragraph. It is the last one-sentence paragraph that is the problem. Our statement of faith is definitely Biblical Theology because it goes no further than the scriptures allow. However, modern "Systematic Theology" adds to the Bible, man-made doctrinal extrapolations from the Bible and philosophical/theological ideas developed over time from the days of the Apostles until now.
Here is a link to our Statement of Faith which must be classified as "Biblical Theology":
Statement of Faith: https://www.thisisyourbible.com/library/show/1139
I hope you have found this helpful.