It's possible that the "balls" were the product of the oak gall wasp.
https://www.google.com/search?rlz=1C1CHBD_en-GBGB788GB788&ei=M83EXJrGK-uJ1fAPlLaDyA4&q=oak+gall+wasp&oq=oak+gall+ink&gs_l=psy-ab.1.4.0i71l8.0.0..6583...0.0..0.0.0.......0......gws-wiz.QDcJROBK_m0