The court judgement addresses this exact point. There are previous judgements (Breyer v Bundesrepublik Deutschland) that establish that dynamic IP addresses are personal data. There are reasonable means to identify the data subject with the help of third parties, such as the ISP. “For this it is sufficient that the defendant has the abstract means for identification of the person behind the IP address. Whether the defendant or Google have the concrete means for linking the IP address with the plaintiff is irrelevant.”
That there is correlating information like timestamps, useragent strings, or referer headers increases the likelihood of actual identification, but the mere reasonable possibility of identification is sufficient for IP addresses to be personal data.
That there is correlating information like timestamps, useragent strings, or referer headers increases the likelihood of actual identification, but the mere reasonable possibility of identification is sufficient for IP addresses to be personal data.